Apparatus and method for accessing foreign databases in a heterogeneous database system

ABSTRACT

An apparatus and method for accessing foreign processes in a heterogeneous database environment includes a local database server having a heterogeneous services module to selectively send requests to the foreign processes based on their respective capabilities. A client application sending a statement to the local database server is checked by the local server process to determine if the statement includes a reference to a foreign database system, or whether the statement is registered as an external routine. The heterogeneous services module selectively outputs a request to an agent process executing in an address space separate from the local server process and in communication with the foreign database. The agent process performs all necessary interaction with the foreign database, including data type translation. The agent includes a conversion module that includes data type conversion routines, and which may obtain additional conversion routines via an Application Programming Interface (API) from a foreign database driver corresponding to the foreign database. The converted request is output from the agent process to the foreign database. Hence, the heterogeneous services module manages client statements involving foreign database systems having limited capabilities, as well as client statements having expressions unrecognizable by the local database server. Use of the agent process ensures that the integrity of the local server process is protected.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to commonly-assigned, application Ser. No. 08/880,326, now U.S. Pat. No. 5,987,463 filed even date herewith, entitled “Apparatus and Method for Calling External Routines in a Database System,” inventors Jacco Draaijer, Roger Bodamer, and Eric Voss, the disclosure of which is incorporated in its entirety herein by reference.

This application is related to commonly-assigned, application Ser. No. 08/880,325, now U.S. Pat. No. 6,041,344 filed even date herewith, entitled “Apparatus and Method for Passing Statements to Foreign Databases by Using a Virtual Package,” inventors Roger Bodamer, Jacco Draaijer, Eric Voss, Raghu Mani, the disclosure of which is incorporated in its entirety herein by reference.

This application is related to commonly-assigned, application Ser. No. 08/880,327 now abandoned filed even date herewith, entitled “Apparatus and Method for Transparent Access of Foreign Databases in a Heterogeneous Database System,” ,”. inventors Roger Bodamer, Jacco Draaijer, Eric Voss, Raghu Mani, the disclosure of which is incorporated in its entirety herein by reference.

FIELD OF THE INVENTION

This invention relates to database systems and, more specifically, to an apparatus and method for interacting with foreign databases in a heterogeneous database environment.

BACKGROUND OF THE INVENTION

Heterogeneous database environments are environments that contain different, and often incompatible, types of database systems. These different database systems are typically purchased independently by businesses to serve a particular need, function or use of the data. As a result, businesses may have information spread across multiple database management systems. Since every database management system vendor attempts to provide a competitive edge over the offerings of its competitors, the different database management systems are almost by definition incompatible. Even database systems based on SQL language standards and the relational model will be incompatible due to differences in SQL implementations, database definition and communication mechanisms. Incompatibility problems are even more apparent between modem relational database management systems and legacy database management systems that use a hierarchical or network architecture. Hence, the task of combining incompatible database systems is extremely complex.

One prior method for integrating foreign databases or data storage in a heterogeneous environment is depicted in FIG. 1A. FIG. 1A is a diagram of a heterogeneous environment having a database application 10 configured to communicate with foreign databases 12 and 14. The database application 10 from one vendor communicates with the foreign database systems 12 and 14 of other vendors using hardcoded instructions 16 and 18 for the foreign databases 12 and 14, respectively. However, this arrangement is limited from an extensibility and scalability point of view, since every application in the heterogeneous environment must be rebuilt with new hardcoded instructions every time an unfamiliar foreign database is added to the heterogeneous environment. Hence, the application 10 would not be able to access a foreign database if the particular instructions for the data format and definitions of that foreign database were not coded directly into the application 10.

Another prior method is shown in FIG. 1B, where a database system 20 accesses the foreign databases 12 and 14 via a gateway 22. The gateway 22 allows client applications to access the foreign databases by translating data and SQL statements having the format of the database system 20 into formats that are recognizable by the foreign database systems. Specifically, the gateway 22 maps the data representation and functionality of one data source onto another data source, performing a translation of SQL statements from the database system 20 into a syntax recognizable by either the foreign database 12 or the foreign database 14. The gateway 22 then sends the translated commands to the targeted foreign database, maps the resulting data from the targeted database into the format of the database system 20, and sends the resultant data back to the database system 20.

Use of the gateway 22, however, suffers from the disadvantage that the mapping mechanisms in the gateway 22 tend to support only the most basic functionality that is common to all of the various databases. Hence, the functionality level of the mapping mechanism is effectively lowered to the lowest common denominator within the group of databases supported by the gateway 22. In addition, SQL mapping by the gateway 22 cannot be performed dynamically, requiring the mapping definitions to be regenerated each time a new and unrecognized foreign database is added. Finally, database performance may be effected since the gateway 22 adds another layer of complexity between the application and the foreign databases.

SUMMARY OF THE INVENTION

There is a need for an arrangement that provides scalable integration of foreign databases in a heterogeneous database environment, where operations necessary for execution of a client statement are selectively translated and sent to a foreign database system based on the corresponding capabilities of the foreign database system.

There is also a need for an arrangement that enhances a local database system in a heterogeneous database environment by integrating operations of foreign databases and external routines with the local database system routines while simultaneously insulating the local database system from potential failures in the foreign databases and external routines.

These and other needs are attained by the present invention, where an agent process provides an interface between foreign processes, executing operation requests sent by the agent process, and a local server process completing execution of a client statement based on results received by the agent process.

According to one aspect of the invention, a computer system configured to respond to a statement includes a local server process and an agent process. The agent process is configured for selectively sending an operation request received from the local server process, necessary for execution of the statement, to a foreign process, and the local server process is configured for completing execution of the statement based on results received from the foreign process. The agent process thus acts as an interface between the local server process and the foreign process, capable of exchanging query statements and query results between the two processes, as well as coordinating distributed transactions between the two processes.

According to another aspect of the present invention, a method for processing a statement from a client includes receiving the statement by a local database server, the local database server having a heterogeneous services module configured to selectively dispatch a request to an agent process in communication with a foreign database server. At least one operation is determined to be performed by the foreign database server to execute the statement, and the heterogeneous services module sends the request to the agent process, which sends the request to the foreign database to perform the at least one operation. The local database server completes execution of the statement based on results received from the agent process interfacing with the foreign database server. The heterogeneous services module thus sends the request to the agent process interfacing with the foreign database based on the relative capabilities of the foreign database. An additional feature is that the heterogeneous services module provides scaleability by sending different requests via a standardized interface to a plurality of foreign databases based on their respective capabilities.

Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings in which like reference numerals refer to similar elements and in which:

FIGS. 1A and 1B are block diagrams illustrating prior art implementations of integrating foreign databases in a heterogeneous database environment.

FIG. 2 is a block diagram of a computer system that may be used to implement an embodiment of the invention;

FIGS. 3A and 3B are diagrams illustrating a database server architecture for a heterogeneous database environment according to an embodiment of the present invention;

FIGS. 4A and 4B are diagrams illustrating alternative implementations of the database server architecture of FIG. 3A in a distributed environment;

FIG. 5 is a diagram illustrating the steps of registering a foreign process to the database server architecture of FIG. 3A;

FIG. 6 is a diagram illustrating the method for processing a statement from a client according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A method and apparatus for processing statements by accessing foreign processes is described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the present invention.

Hardware Overview

Referring to FIG. 2, it is a block diagram of a computer system 100 upon which an embodiment of the present invention can be implemented. Computer system 100 includes a bus 101 or other communication mechanism for communicating information, and a processor 102 coupled with bus 101 for processing information. Computer system 100 further comprises a random access memory (RAM) or other dynamic storage device 104 (referred to as main memory), coupled to bus 101 for storing information and instructions to be executed by processor 102. Main memory 104 also may be used for storing temporary variables or other intermediate information during execution of instructions by processor 102. Computer system 100 also comprises a read only memory (ROM) and/or other static storage device 106 coupled to bus 101 for storing static information and instructions for processor 102. Data storage device 107 is coupled to bus 101 for storing information and instructions.

A data storage device 107 such as a magnetic disk or optical disk and its corresponding disk drive can be coupled to computer system 100. Computer system 100 can also be coupled via bus 101 to a display device 121, such as a cathode ray tube (CRT), for displaying information to a computer user. Computer system 100 further includes a keyboard 122 and a cursor control 123, such as a mouse. The present invention is related to the use of computer system 100 to process statements by accessing foreign processes. According to one embodiment, the processing of statements by accessing foreign processes is performed by computer system 100 in response to processor 102 executing sequences of instructions contained in memory 104. Such instructions may be read into memory 104 from another computer-readable medium, such as data storage device 107. Execution of the sequences of instructions contained in memory 104 causes processor 102 to perform the process steps that will be described hereafter. In alternative embodiments, hard-wired circuitry may be used in place of or in combination with software instructions to implement the present invention. Thus, the present invention is not limited to any specific combination of hardware circuitry and software.

Heterogeneous Architecture

FIGS. 3A and 3B are diagrams summarizing an architecture for a database server process in a heterogeneous environment according to an embodiment of the present invention. FIG. 3A illustrates the overall architecture 150, and FIG. 2B illustrates a diagram of metadata definitions for use by the database server, described below. As shown in FIG. 3A, a client process 200, for example an application program, supplies a statement such as a SQL statement to a local server 202. The local server 202 includes routines for providing the basic services necessary for performing local server operations, for example memory services or context services. The local server 202 performs conventional query processing when processing native requests for data directly accessible by the local server 202, for example data stored in a local database 306. In a “homogeneous database system,” the local server 202 can coordinate with a remote server from the same vendor in a distributed environment for coordinating commitments to respective transactions.

As described in detail below, the client statement may require an operation to be performed by a non-native (i.e., foreign) process, such as a foreign database server (FDS) 208 or an external routine. For example, the client statement may request data from a foreign database 308 under the control of a foreign database server 208. In this case, the local server 202 cannot complete execution of the statement without receiving the data from the foreign database server 208. Alternatively, the client statement may also include a request to be performed by the foreign database server 208 but without returning data, for example creating a new data table or updating data in the foreign database 308. The client statement may alternatively include a call to a procedure that is implemented by the foreign database server 208, but not by the local server 202.

The client statement may also call an external routine that extends the capabilities of the local server 202 beyond a standard set of commands.

Specifically, users interact with many database systems by submitting SQL statements to the database systems. To supplement the functionality of a limited standard set of SQL commands, external routines (i.e., “extensions”) can be coded, potentially by third parties, in a third generation language (3GL) such as C or C++. However, it is desirable to control the execution of the external routines to ensure that failures in the external routines do not adversely affect the local server 202. For example, a common bug in a C function de-references an invalid pointer and causes a segmentation fault, resulting in a crash.

The heterogeneous architecture of FIG. 3A includes heterogeneous services modules 311 and 311′ that augment the distributed functionality of the local server 202 to enable non-native database servers 208 to be incorporated into the distributed architecture. The module 311 is executed in the local server process 311 and the module 311′ is executed in an agent process 300. The local server process 202 communicates with the agent process 300 via a remote process mechanism in the foundation services 204. The foundations services 204 perform the basic services that are needed for processing heterogeneous operations. The basic services include memory handling, establishing the proper context (e.g., login and logoff), and the remote process mechanism. The remote process mechanism provides a framework that allows the local server 202 to operate in a heterogeneous environment (e.g., a distributed system having servers from different vendors).

The agent process 300 also enables external routines (e.g. C functions) stored in a dynamically-linked library (DLL) 314 to be executed without concern of crashing the local server 202. Thus, the agent process 300 provides an interface between the local server 202 and a foreign database server 208 that ensures that any operation of the foreign database server 208 will not adversely affect the local server 202. Furthermore, the agent process 300 may execute a driver 214, which has been provided by a third party such as the vendor of the foreign database server 208. Hence, the local server 202 is insulated from the routines executing in the agent process 300 to protect the local server 202. If the external routines executing in the agent process 300 are later deemed reliable or safe, the remote process mechanism can be removed and code for the agent process 300 can be linked directly into the local server 202.

The agent processes 300 are separate processes, started by the heterogeneous services 311 of the local server 202 and executed in an address space separate from the local server 202. Hence, the agent process 300 protects the local server 202 from crashes that may occur in the agent process 300 during execution of a non-native routine. In addition, the agent process 300 may be executed on a machine separate from the local server 202.

The heterogeneous services modules 311 and 311′ enable the local server 202 to complete execution of client statements that require execution of non-native operations. Specifically, the local server 202, upon receiving a client statement having a database link to a remote process, will access a remote link table that is stored on the file system of the local server 202. The remote link table includes information that specifies how to a point to a communication link to a remote process based on the database link specified in the client statement. Specifically, the remote link table uses the database link as an alias to identify (1) the remote process executing on a remote machine, (2) link-related information such as network address, TCP/IP port number, etc., to find out exactly which process to connect to, and (3) whether the database link points to a foreign system. If the remote link table specifies that the referenced database link points to a foreign system, the local server 202 will invoke the heterogeneous services using the first heterogeneous services module 311 in the local server 202, which in turn invokes the second heterogeneous services module 311′ in the agent process 300.

The first heterogeneous services module 311, which is built upon the foundation services 204, performs all possible operations that do not require the interaction of the external process. For example, the first heterogeneous services module 311 helps identify an operation necessary for execution of the client statement that must be executed by an external process (e.g., an external routine or a foreign database system), and forwards the identified operation to the appropriate agent process 300 via the identified remote path for execution. As described below, the first heterogeneous services module 311 includes specific services modules for controlling respective operations.

The agent process 300 includes foundation services 204′ that complement the operations of the foundation services 204 in the local server 202. For example, the foundation services 204′ maintains the communication path 310 with the local server 202 by handling the requests received from the local server 202 and sending results during execution of the agent process 300 to the local server 202. The communication path 310 can be a shared memory or other inter-process connection or a network connection. The second heterogeneous services module 311′, which is built upon the foundation services 204′, manages the operations requiring interaction with the third-party code, whether the third-party code is an external routine stored in the dynamically linked library 314, or a driver communicating with the foreign database server 208. Hence, the first heterogeneous module 311 will perform all operations that do not require an actual interface or interaction with third-party code, whereas the second heterogeneous module 311′ will preferably perform only those operations associated with interacting with the third-party code, such as data translation between the conversion module 211 and the third-party driver 214 or execution of a third-party external routine from the library 314.

The first heterogeneous services module 311 includes a plurality of modules that enable the local server 202 to interact with the foreign processes via the appropriate agent process 300. Specifically, the heterogeneous services include a transaction services module 210 a, a SQL services module 210 b, a stored procedures module 210 c, and an external procedures module 210 d. As described below, the heterogeneous services in the local server 202 also include a passthrough SQL module (PSM) 207 that operates separately from the modules 210. Each of the modules 210 a, 210 b, 210 c, and 210 d, are built upon the foundation services 204, and are integrated with the local server 202 to use services within the local server 202, as shown by the dotted line 209 in the heterogeneous services.

The dotted line 209 refers to a native API interface, described below, used by the local server 202 to issue calls to a remote server. Instead of sending the API calls directly to the foreign database system 208, the heterogeneous services module 311 intercepts the calls to the foreign database system 208 and remaps the API calls by the local server 202 to a generic API 212. The heterogeneous services module 311 will then issue a remote procedure call to the agent process 300 to call a selected function in the driver 214. The agent process 300 will then call the selected function in the driver 214 (e.g., “parse”).

Each of these modules 210 in the heterogeneous services module 311 is configured to map a particular database operation to a target foreign process based upon the operation specified in the client statement and based upon metadata definitions metadata for the heterogeneous services stored within a data dictionary 220, described below. As shown in FIG. 2B, the data dictionary 220 includes metadata definitions for use by the foundation services 204, as well as for the different modules 210 and 207.

There are four types of translations that may occur between the local server 202 and the foreign database server 208. The first type of translation relates to the Application Program Interface (API) of a given database system. Specifically, an API is a set of functions, procedures, or routines specific to a module, such as an application or library, that can be called by an external module to communication with the module. For example, Oracle has a set of API referred to as OCI API, where functions such as “oopen”, “oparse”, “oexec”, “ofetch”, and “oclose” correspond to the functions of opening a cursor, parsing a SQL statement, executing the cursor, fetching results, and closing the cursor, respectively. However, one database system (e.g., Oracle) will have its own API set, while another database system (e.g., Sybase) will have its own API set. Since the API for each database system can be completely different, it becomes particularly difficult to develop any systematic translation scheme.

Hence, the first type of translation, executed by the heterogeneous services module 311 in the local server 202, maps the native API protocol (e.g., Oracle API) onto a generic API, identified as the HS API 212 in FIG. 3A. The driver 214 for a specific foreign database server 208 can then map the generic API 212 to the API set of the foreign database server 208.

A second type of translation relates to SQL statements, which are highly structured. Hence, although a SQL statement in the format of the local server 202 may not be acceptable to the foreign database system 208, the structured nature of a SQL statement enables the heterogeneous services modules 311 to convert the SQL statement of the local server 202 to the format of the foreign database system 208 using a SQL services module 210 b. In addition, API functions such as “parse” are performed by a majority of database systems. Hence, a generic function such as “parse” for a certain SQL statement can be passed to the foreign database system 208 using the modules 311 in the local server 202 by translating the SQL statement from the native (local server process 202) format to the format of the foreign database system 208. The translated SQL statement in foreign database system format can then be passed as an argument of a generic function (e.g., parse). For example, an SQL statement translated by the SQL services module 210 b can be an argument for the Oracle-specific call “opiosq,” which is then mapped onto the generic API 212 as “parse.” Thus, the generic function is called at the HS API 212 having the translated SQL statement as an argument. The driver 214 then can map the generic function onto the foreign database system API, while including the translated SQL statement as the argument.

A third type of translation relates to data types, where the local server 202 represents data (e.g., dates) in a different format than the foreign database system 3208. Hence, data must be converted in the agent process 300 if the local server 202 is fetching results from the foreign database system 208, or sending or receiving bind variables to and from the foreign database system 208. This data type translation is executed in the agent process 300 by a conversion module 211.

A fourth type of translation is data dictionary translation, executed in a SQL services module 210 b within the heterogeneous services module 311 of the local server 202. Every relational database has its own set of data dictionary tables which store various kinds of information (known as “metadata”) about the objects in the database created by its various users. This set of tables along with views defined on them are together called the “data dictionary”. As a user makes modifications to his schema (for example, creating or deleting a table), the local server 202 will keep track of the modification by automatically adding or deleting entries in one or more tables of the data dictionary. The foreign database system 208, however, may include similar metadata that is organized differently. In order to make the foreign database system 208 appear to the client 200 as homogeneous relative to the local server process, the client must be given the impression that the metadata in the data dictionary of the foreign database system 208 is in the same format as in the data dictionary of the local server 202. For example, assume the data dictionary for the local server process 202 includes a table entitled “user_catalog,” and the client 200 issues a query on “user_catalog @ FDS”, where “FDS” is an identifier for foreign database system 208. However, if the foreign database system 208 does not have the table “user_catalog”, but rather the metadata is spread across different tables, the client 200 is given the appearance that the table exists at the foreign database system 208 in the structure perceived by the client.

Hence, the data dictionary translation gives the appearance to the client that the foreign database system 208 includes metadata in the format and structure as stored for the local server 202. Thus, the heterogeneous services modules 311 and 311′ map the query to accommodate the data dictionary structures in the foreign database system 208, get the result back from the foreign database system 208, and return the results to the client 200 in the format of the local server 202.

In an example of a data dictionary translation from an Oracle server to a Sybase server, the heterogeneous services modules 311 and 311′ convert the client statement “select table_name, table_type from user_catalog @link” to a Sybase-compatible query, for example:

select SO.name table_name,

substr(‘TABLE’,1,5*(1-abs(sign(ascii(SO.\“type\”)-ascii(‘S’)))))∥

substr(‘TABLE’,1,5*(1-abs(sign(ascii(SO.\“type\”)-ascii(‘U’)))))∥

substr(‘VIEW’,1,4*(1-abs(sign(ascii(SO.\“type\”)-ascii(‘V’)))))∥

table_type

from sysusers@link SU, sysobjects@link SO

where SU.UID=SO.uid and SU.name=USER@link

This gives the client 200 the impression that there actually is a table called “user_catalog” at the remote server and that it actually does have columns called “table_name” and “table_type,” when actually the information is extracted from two Sybase data dictionary tables “sysusers” and “sysobjects”.

Hence, the data dictionary for the local server 202 may include tables that are not found on in the data dictionary of the foreign database system 208. If the local server 202 receives a query from client 208 referencing one of these tables with respect to foreign database system 208, the local server 202 first attempts to use that table on the foreign database system 208. If the table does not exist at the foreign database system 208, an error is returned and, in response, the heterogeneous services module 311 checks a data dictionary translation table (DDX) 231. If translation information is found, the query is translated and sent to the foreign database system 208 via the agent 300. The results of the query from the foreign database system 208 are then translated before being back sent to the client 200.

Another aspect of data dictionary translation occurs when a data dictionary table for the local server 202 includes information that is not present in the referenced foreign database system 208. Assume that a client statement includes a reference to a data dictionary table at the foreign database system 208, in which the information does not exist at the foreign database system 208 according to the capability table 224 and the DDX 231. To give the client 200 the appearance that the table exists in the foreign database system 208, the DDX 231 may include a reference for the heterogeneous services module 311 to mimic the existence of the table in the foreign database system 208 by going to the local database and requesting from the local database the definition of the requested table. The heterogeneous services module 311 then returns to the client 200 (via the local server 202) the definition of the table. If the client 200 requests information, the local server 202 will return an error message that no rows are selected.

Hence, all the translations are performed by the heterogeneous services module 311 in the local server process, except for the data type conversion, which is performed in the agent process 300.

The agent process 300 includes services and routines to carry out prescribed operations for the local server 202. Specifically, a plurality of different agents 300 can be initiated by the heterogeneous services of the local server 202 to interact with respective foreign database servers 208. For example, one agent 300 a may interact with a Sybase database system, and another agent 300 b may interact with an Informix database system, etc. Each agent 300 includes the foundation services 204′ and a conversion module 211, described below. Each agent also includes a corresponding set of services modules 210 a′, 210 b′, 210 c′ and/or 210 d′ that correspond to the capabilities of the corresponding foreign database system. Hence, if a foreign database server 208 does not have transaction services, the corresponding agent 300 interacting with that foreign database server 208 will not need a transaction services 210 a′. Alternatively, the transaction services 210 a′ may be available in the compiled code for the agent process 300 but unused because the metadata stored in the data dictionary 220 does not identify that foreign database system as supporting that service.

The conversion module 211 provides the data translation services necessary for converting from the data format native to the local server 202 to the data format of the target system 208. Three types of data type conversion are possible. In the first type, the conversion module 211 contains all the necessary conversion routines to convert from the native data type of the local server 202 to the data type of the target system 208. In the second type, the conversion module 211 converts from the native data format based on routines supplied by a driver 214, where the conversion routines within the driver 214 may be supplied, for example, by the manufacturer of the target system 208. In the third type, the native data type is described in terms of an intermediate data type to perform an n-step conversion. For instance, one of the steps is performed by a conversion originally supplied with conversion module 211 and another of the steps is performed by a conversion function registered by the driver 214. Regardless of the conversion type, the data type translation is performed in the agent process 300, transparent to the local server 202.

In the case of the second and third type of data type conversion, the driver 214 registers conversion routines having a predetermined prototype with the conversion module 211. The predetermined prototype specifies the number and type of the arguments of a conversion routine as well as the type of the return value, if it exists. Thus, the conversion module 211 sends data (i.e., an array of numbers) invokes a registered conversion routine of the driver 214 for translating the data to the format of the foreign database system. Alternatively, the driver 214 may specify an intermediate n-step conversion, where the conversion module 211 translates from the native data type to an intermediate data format specified by the driver 214, enabling the conversion routine of the driver 214 to convert from the intermediate data format to the internal format of the foreign database system 208. The intermediate date format can be an industry-standard data format, such as the ISO date format, to simplify the development of the driver 214 by third parties.

Thus, the local server 202 uses the heterogeneous services to output an operation request (e.g., an API call or an SQL statement) to a target foreign database (e.g., foreign database 208) by sending the request to the agent process 300. The conversion module 211 in the agent process 300 converts the data types to the format of the foreign database server 208, using internal conversion routines or registered routines supplied by the driver 214. Use of the agent 300 to execute registered routines supplied by the driver 214 thus protects the local server process 202 from crashes. The translated data in the foreign format is output from the agent process 300 to the foreign database server 208 to process the operation request. Once the foreign database server 208 generates results based upon processing the operation request, the data results are translated by the conversion module 211 to the data type of the local server 202 in accordance with the appropriate services module 210′. The local server 202 can then complete execution of the client statement based upon the results received from the foreign process 208 b.

FIG. 3B is a diagram illustrating a part of a data dictionary 220 providing metadata definitions for heterogeneous services. The data dictionary 220, stored in the local database 306, enables the local server 202 to determine how to process a received client statement. As described below, a foreign server 208 can be accessed either by referencing the specific foreign system, by referencing the heterogeneous services 210 configured to identify the appropriate foreign system, or by providing the local server 202 with definitions enabling the local server 202 to independently identify a call to a foreign server 208. The data dictionary 220 includes an initialization table 222 that specifies the information needed to startup and initialize an agent and connect it to a foreign database server 208. The initialization table 222 is used by all the services, including the foundation services 204, the transaction services 210 a, the SQL services 210 b, the stored procedures 210 c, and the external procedures 210 d. The values are defined partly by the heterogeneous services, and partly by the corresponding driver 214.

The data dictionary 220 also includes a capability table 224. The capabilities table 224 specifies the capabilities of the target system 208. For example, the capabilities table 224 includes a transaction services model 224 a that describes the transaction model of the target system 208. Transaction models of target systems range from just read-only support at one end to full two-phase commit support at the other end. The SQL translations (SQL X) services model 224 b provides SQL translation information on how to translate SQL functions in the local server 202 onto the functions of the target system 208 for the SQL services module 210 b and the stored procedures module 210 c, described below. The data type translations (DTY X) model 224 c provides information on how to map foreign data types to data types native to the local server 202 for the SQL services module 210 b and the stored procedures module 210 c, as well as the conversion module 211.

The data dictionary 220 also includes a distributed external procedures security table (SEC) 226 and a distributed external procedures mapping data table (DEP MD) 228. The SEC table 226 stores information about users that have privileges to create, drop, alter, and/or execute a distributed external procedure, and the DEP MD table 228 contains information to map a PL/SQL function onto a distributed external procedure, such as a C function. The information in the DEP MD table 228 may include data types, number of arguments, the name of the function, indicator values, etc. Thus, the DEP MD table 228 stores metadata that is not relevant to the local server 202, but which is necessary to perform the distributed external procedure as it is passed to the agent process 300.

The data dictionary 220 also includes a data dictionary translation table (DDX) 231, described above, that contains a list of data dictionary table names and respective translation instructions for the data dictionaries in the foreign database system 208. The translation instructions will include the translation (mapping) information on how to map from the native data dictionary tables to the data dictionary tables of the foreign database system. Alternatively, if the foreign database system 208 does not include the corresponding metadata, the DDX 231 will include a mimic instruction for the corresponding mapping.

The data dictionary 220 enables the local server 202 to determine the relative capabilities of a target foreign server to process a statement in the agent process 300, and thus enables the local server 202 to call the appropriate services 210 to obtain the desired result.

The heterogeneous services in the local server 202 of FIG. 2A are performed by modules 210 that are built upon the foundation services 204 and integrated with the local server 202. The SQL services module 210 b, also referred to as a query services module, controls translation of SQL statements identified for execution by a foreign database server 208 to the corresponding foreign format.

Specifically, assuming that the client statement includes a SQL statement recognized by the local server 202 as referencing data in a foreign database (e.g., foreign database “DB_A” 208 a), the local server 202 parses the SQL statement into operations necessary for execution of the statement. The DTY X table 224 c provides the data translations to translate the data object definitions. The SQL services module 210 b obtains the mapping information from the DTY X table 224 c, and sends the mapping information to the agent process 300 for the conversion module 211 to perform the data type translation.

Hence, all the translation information is stored in a table in the local database 308. The mapping information stored in the data type translation table 224 c is then sent by the HS 311 to the agent 300 for data type translation.

The transaction module 210 a is configured to coordinate transactions between the local server 202 and the corresponding foreign server 208, for example distributed transactions such as a two-phase commit transaction as performed in current commercially available Oracle database systems. Based on the capabilities specified in the capabilities table 224, the transaction module 210 a can make transaction related calls, such as “begin transaction,” “end transaction,” and “commit,” to the agent process 300. The corresponding module 210 a′ passes these generic transaction calls on to the driver 214, which maps the transactions calls into transaction calls appropriate for the target system 208.

The stored procedures module 210 c is used to perform a “describe operation” dynamically for an operation within the client statement. Specifically, the local server 202 sends a request to the target system 208 to describe the specified operation, and will receive a response that describes the number and types of the parameters for performing the operation. For example, a procedure may be described as having five prescribed arguments. The response enables the stored procedures module 210 c to determine how to use the SQL services module 210 b for data type conversions. Thus, the stored procedures module 210 c enables a function to be invoked at the target system 208 (via the agent process 300) by identifying the operation to be performed, specifying the arguments, and requesting that the operation be executed. This module is thus particularly helpful for executing stored procedures (e.g., fourth-generation (4GL) routines) in the target system 208.

The external procedures module 210 d is configured to control execution of external procedures, also referred to as external routines, for which there is not a description of the function provided by a foreign database server 208, but rather is intended to be executed as an enhancement to the local server 202. In other words, the external routine is implemented as a C function that is incapable of describing itself. In this case, the metadata needs to be separately generated based on an analysis of the function and stored either in the local database for external procedures or in the DEP MD table 228 for distributed external procedures. Once the metadata for the external routine is available, the external routine can be called by causing the agent process to call the external routine from a specified address in the DLL 314, followed by passing of any necessary parameters to the agent process 300.

According to the disclosed embodiment, the local server 202 may selectively use any of the services modules 210 a, 210 b, 210 c, or 210 d to perform a certain operation. For example, the transaction services 210 a may be used in combination with the SQL services 210 b for a database gateway. The external procedures 210 d may be used with the transaction services 210 a for distributed external procedures.

FIG. 4 is a diagram illustrating an exemplary implementation of the heterogeneous architecture of FIG. 3. Specifically, the agent process 300 may be executed in a second processing system 322 separate from the first processing system 304 executing the local server 202. In such an arrangement, the local server 202 accesses local data using solely the first processing system 304 by accessing a local database 306. However, if local server 202 needs to access foreign data in a foreign database 308, the local server 202 communicates with the agent process 300 via a network connection 310. For example, the statement from the client application 200 may be a SQL statement “select * from table@FDS,” where “FDS” is identified by the local server 202 as a reference to the foreign database system 208. If there is no prior connection with the remote computing system 302, the foundation services 204 will establish a connection 310 to a listener agent of the remote computing system 302, which will spawn the agent process 300. The foundation services 204 will then initialize the agent 300, log on for verification (e.g., log on using a user name and password), and send the statement to the agent process 300. The agent process 300 receives the statement from the local server 202, and uses its foundation services 204′ and associated modules 210 and 211 (shown generically as “HS Generic” 311′) to send the appropriate statement to foreign server 208. If the conversion module 211 does not have its own internal conversion routine, the agent process 300 will send the translated request to the foreign server 208 via the API 212 using the foreign database driver 214.

The arrangement of FIG. 4A enables distributed processing between the local server 202 and the foreign server 208, where the heterogeneous nature of the statement processing (i.e., between a native system and a foreign system) is transparent to the client application 200. Specifically, the arrangement of FIG. 4A enables transparent heterogeneous processing, where the local server 202 completes execution of a statement from the client 200 based upon at least one operation executed by the foreign server 208 that is necessary for processing of the statement by the local server 202, while maintaining the appearance to the client application 200 that the operation is performed by a remote server in the same native system, i.e., a homogeneous distributed database system in which all database servers are from the same vendor. This arrangement, also referred to as “transparent SQL processing,” enables the local server 202 to process at least a portion of the client statement using the foreign server 208, while maintaining the appearance to the client application 200 that the processing of the client statement at a remote site uses a remote server from the same vendor as the local server 202. Hence, if the local server 202 is an Oracle server process, the FDS system 208 (e.g., Sybase, Informix, etc.) will appear to the client as a remote Oracle server process. As described below, the passthrough module maps the foreign client statement to the API 212 by bundling a series of calls to the foreign database system 208, enabling the agent process 300 to supply one call having multiple bind variables, described below, as opposed to multiple single-variable calls.

Whereas the local server API 209 and the generic API 212 are based on C functions, the passthrough SQL API 265 for the passthrough module 207 includes a set of enhanced procedural SQL functions executable by the local server process, for example PL/SQL functions provided by Oracle Corporation. These passthrough SQL API 265 functions can be called by the client 200 by passing as an argument the foreign SQL statement to be executed by the foreign database system 208. As far as the local server 202 is concerned, the client 200 is issuing a call to a remote API function (e.g., using PL/SQL) that includes certain arguments. Thus, the local server 202 submits the call to the remote database system (in this case foreign database system 208) for execution, without examining the contents of the call.

Hence, a “parse” call for a supplied foreign SQL statement can be made to the foreign database system 208, without the local server 202 knowing that the parse call has been made.

Hence, the client 200 executes a statement that calls a function of the passthrough SQL API 265. The local server 202 identifies the passthrough SQL API 265 statement as an operation to be performed at a remote site, because the statement includes a link name. Information associated with the link name identifies the heterogeneous services module 311 including the passthrough SQL module 207. The local server 202 then passes the client statement to the heterogeneous services module 311, which performs the necessary processing in the passthrough SQL module 207. As far as the local server process 202 is concerned, the client statement is a passthrough SQL API 265 function. Since the actual foreign SQL statement is an argument to the passthrough SQL API function, the foreign SQL statement will not be parsed by the local server 202.

The local server 202 submits the call by the client 200 to the heterogeneous services module 311, which intercepts the passthrough SQL API 265 call and maps the call onto the generic API 212. As a result, the number of relatively expensive network calls from the local server 202 to the foreign database system 208 can be minimized, especially where a passthrough SQL call by a client may include a bind value (e.g., a data value). Specifically, each individual passthrough SQL call invoked by the client 200 is not necessarily sent to the foreign database system 208, but collected into one multiple bind statement. After all bind calls from the client 200 (or from multiple clients 200) are received by the passthrough module 207, a single call is made from the collected bind variables to the generic API 212. Hence, the collection of bind variables by the passthrough SQL module 207 provides a much more efficient arrangement, since the single call to the generic API 212 is particularly efficient, especially for network traffic, resulting in considerable gains for performance.

FIG. 4B is a diagram illustrating an alternative implementation of the architecture of FIG. 3A, where a client application 200 sends a statement to the local database server 202 calling a external routine executed in a separate agent process 300. External routines can be used to allow the client application 200 to access the foreign server 208 using a custom function written in a third generation language, such as C or C++. As shown in FIG. 4B, the local server 202 initiates a connection via a communication path 310 with the agent process 300 that is executing in an address space separate from the address space of the local server 202. The agent process 300 accesses the appropriate external routine stored in a DLL 314. Specifically, the local server 202 initiates the connection with the agent process 300, and causes the agent to execute the external routine stored in a DLL 314 in order to perform the necessary operation. The agent process 300 executing the external routine thus communicates with the foundation services 204 which provides arguments for the agent process 300. The agent process 300 executes the operations specified by the local server 202, for example by interacting with the foreign server 208 to obtain data from the foreign database 308.

Distributed external routines are coded in a third generation language. The external routine is then archived in an operating system DLL 314. The DLL 314 is then registered within the data dictionary 220 within the local database server 202, and the external routine is then registered within the data dictionary 220 as stored in the DLL 314.

FIG. 5 is a diagram illustrating steps to register a foreign server 208 with the local database server 202 for establishing the heterogeneous architecture of FIG. 3. A connection to the foreign server 208 is first established by registering an agent in step 400, enabling the foundation services 204 to set up a communication path 310 with the foreign system 208 via the corresponding agent process 300. As recognized in the art, commercially available listener agents can be configured to set up the agent process 302 based upon standardized API instruction sets. As described below, the listener agent (not shown) may control the initiation and connection of multiple agents to the local server process 202. Alternatively, the functions of the listener agent may be performed by the foundation services 204.

Once the listener agent (or the foundation services 204) has been configured in a way to start up the agent process 300, the data dictionary 220 is installed in step 402. Class information is then installed in the data dictionary table 220 in step 404. The data dictionary 220 stores class and instance information that identifies the capabilities of the foreign system and the objects corresponding to the foreign system 208, respectively. For example, the capabilities table 224 stores the foreign system capabilities, SQL translations, and the initialization table 222 stores initialization parameters, etc., for each foreign system as groups of classes to minimize unnecessary redundancy. Specifically, a class defines a type of foreign system. At the same time, instance specific information is necessary for each transaction performed by the local server 202. Accordingly, the capabilities table 224 can store both class and instance-level information. Hence, multiple instances can share the same class information, but each foreign system instance will have its own instance-level information. An example of a class is a foreign system from a particular vendor. Subclasses may also be subdivided within the class, for example, for individual versions of the vendor-specific database systems.

After the capabilities table 224 has been installed with the class information, the foreign system instance 208 is registered in step 406 with a new instance name and the class to be used to access the foreign system.

Instance-specific initialization parameters are then set in step 408 for each instance, for example a domain (virtual path) for a foreign system, a database name for the foreign system, an internal unique name used by the local server 202 for creating distributed transaction identifications, language settings for the foreign system, the maximum number of cursors (i.e., assigned memory spaces) that can be open, and the ability of the foreign system to become a commit point site in a distributed transaction. Agent-specific initialization parameters may also be required, for example, connection information required to connect to a foreign system.

Once the instance-specific initialization parameters have been set in step 408, then desired external routines are installed in the DLL 314 in step 410. The connection is then established in step 412 (e.g., a communication path 310) to test the access to the foreign processes 208.

Heterogeneous Statement Processing

FIG. 6 is a flow diagram illustrating a method for processing a statement from the client 200 according to an embodiment of the present invention. The steps of FIG. 6 illustrate the transparent SQL, passthrough SQL and distributed external routines functionality of the architecture of FIG. 3.

As shown in FIG. 5, the local server 202 receives the statement, for example a SQL statement, in step 500 from the client 200. The local server 202 determines in step 502 whether the client statement includes a reference to a foreign database system, for example if the client statement includes a database link. A database link is an identifier that points to the foreign database system as specified in the remote link table. An example of a database link occurs in the SQL statement “select * from table@DB_A,” where the remote link table identifies the database link “@ DB_A” as a reference for the foreign database system 208. The reference to a foreign database system 208 by the database link implicates the use of heterogeneous services 210.

If the local server 202 determines the client statement includes a reference to a foreign database system 208, the local server 202 submits the client statement to the heterogeneous services 311. Heterogeneous services 311 determine whether the statement includes a call to the passthrough SQL module 207 from the user's schema and the data dictionary 220, step 504. If the client statement is a call using the passthrough SQL module 207, the client statement is intercepted and mapped onto the generic API 212 to the agent 300 corresponding to the referenced foreign database system 208 in step 506, as described above. Specifically, the passthrough SQL module 207 collects bind values from the client 200 before making a call to the generic API 212.

The foundation services 204 establishes the communication path 310 with the agent process 300 in step 506 c. The passthrough SQL module 207 then maps the passthrough SQL API 265 carrying the foreign statement and bundles bind variables as arguments onto a single API 212 call by making a list of bind values corresponding to a set of bind variables. The foundation services 204 also passes any strings (in the format for foreign database system 208) included with the statement from the client 200. The agent process 300 receives the mapped passthrough SQL API call and its arguments (e.g., the foreign statement and any foreign parameters passed via the communication path 310). The generic API 212 submits the bundled passthrough SQL call to foreign server 208, thus minimizing the number of calls to the foreign server 208 for execution.

The agent process 300 receives the results from the foreign server 208 in step 508 into buffers of the heterogeneous services 311′, and passes the results back through communication path 310, in step 510. The results are presented in step 512 to the client 200 in a set of bind variables, each having a corresponding set of bind values. For example, the statement from the client 200 may include the expression “foo( . . . , FDSX, FDSY, . . . )” where the expression “foo(args)” is a function performed by the local server process 202, and the expressions “FDSX” and “FDSY” are expressions specific to the foreign server 208. The expressions “FDSX” and “FDSY” would be passed onto the generic API 212 as “foo( . . . , FDSX, FDSY, . . . )” via the agent 300 in step 506 for processing by the foreign server 208. The results of the processing by foreign server 208 would be received from the agent process 300 in step 508. If the local server 202 recognizes the procedure “foo”, the local server 202 would recognize that the enclosed (but unread) arguments “FDSX” and “FDSY” would cause the referenced foreign process to return results having a specified data type. Accordingly, the local server 202 is able to anticipate the results of the unrecognizable expressions “FDSX” and “FDSY” to be received from the foreign server 208. The local server 202 completes execution of the client statement in 510, and presents the results of the statements to the client in step 512.

As described above, a particular advantage of utilizing the passthrough SQL module 207 and the agent process 300 for the passthrough SQL operations of steps 506, 508, and 510 is that calls for sending data to the foreign server 208 need not be arbitrarily output to the foreign database system 208, thereby increasing the communication between the local server process 202 and the target system 208. Rather, data can be collected, and once a number of requests have been collected, a single call can be made to the target system 208. For example, bind variables enable the same SQL statement to be used multiple times with different values. Hence, if execution of a client statement requires inserting one hundred rows of one hundred columns into a particular table, the SQL statement needs to be parsed only once, and then the database process binds and executes the SQL statement for each row. Hence, the agent process 300 can send a single statement to the foreign server 208 including the bind variables, as opposed to sending a plurality of bind calls.

The architecture 150 also is configured to perform “transparent SQL” functions, where database operations are performed in a foreign server 208 and completed in the local server 202 in a manner that is transparent to the client application 200. As described above, the local server process 202 will determine in step 502 whether the client statement includes a reference to a foreign database system. If the client statement includes the foreign database system reference and the local server process 202 determines in step 504 that the client statement is not a call to the passthrough SQL module 207, the local server process 202 parses the client statement in step 514 to determine a plurality of operations necessary for execution of the client statement.

The local server 202 then identifies at least one of the operations to be performed by the foreign server 208 by accessing the capabilities table 224 in step 516 to compare the relative capabilities of the identified foreign system 208 relative to the operation to be performed. For example, the local server 202 will control the SQL services module 210 b to access the capabilities table 224 in order to determine whether the foreign server 208 can perform a particular query. Alternatively, the local server 202 will control the transaction services module 210 a to access the capabilities table 224 to determine whether the foreign server 208 can perform an operation such as a two-phase commit. If the capability table 224 indicates that the target foreign process 208 is capable of performing the prescribed operation, the heterogeneous services module 311 performs the necessary translations in steps 518 and 520 (e.g., API translation, SQL statement translation, data dictionary translation) and sends the converted operation and the data type translation information to the agent 300 in step 522 for data type translation by the conversion module 211 and the corresponding module 210′.

As an example of the translation, the local server 202 accesses the data dictionary translation table 231 to determine whether a data dictionary table specified in the statement exists for the foreign server 208. For example, a client statement may include the expression “select * from allusers@FDS”, where the data dictionary table “allusers” is defined in the local database 306 but not the foreign database “FDS” 308. The DDX 231 may specify that the database “FDS” 308 has two tables A and B, and that the joining of tables A and B from the foreign database 308 provides the same information as in the “allusers” table defined in the local database 306. Hence, the appropriate module 210 generating the request performs a substitution to convert the SQL statement from “select * from allusers@FDS” to “select * from (select * join A, B)@FDS”, which is then passed to the FDS database in step 522.

If the DDX 231 does not include a reference to a specified table, then the local server 202 checks to see if the user's schema defines the unknown table. If there is no definition for the unknown table in the user schema, then the local server 202 checks its internal data dictionary generally. The DDX 231 includes table definitions that are perceived to be in the foreign database system 208, even though the foreign system 208 may not have the specified table, or the foreign database system may not store the requested information in a compatible database structure. For example, the foreign database may not support object definitions using data dictionary tables. In this case, the DDX 231 table specifies that the unknown table is a mimicked table.

If the DDX 231 indicate in step 519 the objects specified in the client statement need to be mimicked, then the local server 202 will process the request locally in step 521 as a “describe” function, as described above. In such a case, the local server 202 would return to a table with zero rows in step 512. Hence, the mimic function enables the local server 202 to return at least the structure of the table specified in the client statement, as opposed to a global error message without any results to the client statement.

Another type of translation is function translation. For example, suppose that the client 200 issues the statement “select foo(a, b) from table@FDS,” where foreign database system “FDS” does not implement the function “foo,” but there are one or more other functions at the foreign database system what will produce the same result. In this example, assume that foreign database system has two functions, “f1” and “f2,” which can indirectly implement the functionality of “foo.” In this case, function translation results in a statement, such as “select f1(a)+f2(b) from table@FDS.”

Execution is completed in step 528 by the local server 202 before sending the results to the client 200. For example, assume the function “foo” is not supported by the foreign system, as specified by the capabilities table 224. In such a case, the statement “select foo(A, B) from table@FDS” would be parsed by the local server process 202 in step 514, and the SQL services module 21 Ob would generate a request in step 520 as “select A, B from table @ FDS”. Upon receiving the contents of tables A and B from the foreign process database system “FDS” 308 in step 524, the local server 202 completes execution in step 528 by performing the operation “foo” on the results of the query “select A, B from table (FDS”. Thus, the process of executing the function in the local server 202 using data accessed from the foreign database system 308, also referred to as “post-processing,” appears to the client application 200 to be fully executed within the local database server 202, even though agent process 300 extracts the data from the foreign database system 208.

Another kind of post-processing is “post where-clause filtering” in which the where-clause cannot be executed by the foreign system 208. In the above example, the where-clause of query “select A from table@FDS where A=foo(B)” cannot be executed by the foreign system 208, because “foo” is not an operation implemented on foreign system 208. In this case, the query “select A, B from table@FDS” is submitted to the foreign system 208 via agent process 300, and the local server 202 completes the execution of the query by calling the local “foo” operation with the values of A and B received via agent process 300. Thus, post-processing helps make a heterogeneous distributed database system look like a homogeneous database system (e.g., the client process 200 need not know that “foo” is unavailable for foreign system 208), promoting transparency.

The passthrough SQL feature as described with respect to steps 506, 508, and 510 and the transparent SQL feature described with respect to steps 514 through 528 provide an arrangement where at least a portion of a statement received by the local server 202 is executed at the foreign server 208 in a manner such that the fact that the remote operation is performed on a foreign database is transparent to the user. In the case of passthrough SQL, the database link used as part of the identifier, and the agent process 300 acts as a virtual interface for the foreign server 208, since a plurality of foreign statements can be collected by the passthrough module 207 prior to sending the statements to the foreign server 208. The collection of statements is particularly beneficial for bind calls. The agent process 300 gives the appearance to the client 200 for transparent SQL that all operation, including access of data from the foreign database 308 and distributed transactions between the local server 202 and the foreign database 308, is performed within a homogeneous distributed system.

As shown in step 502 in FIG. 6, the passthrough SQL and transparent SQL operations are performed based on detecting in the client statement a reference to a foreign database 308. If there is no reference to a foreign database system, the local server 202 checks in step 532 whether the client statement includes a remote procedure call. Specifically, the local server 202 checks the data dictionary 220 to determine whether the client statement includes a registered external routine. As described above, the DLL 314 is registered in the data dictionary 220, and each external routine stored in the DLL 314 is registered in the data dictionary 220 with respect to the DLL 314.

Upon detecting the statement as a remote procedure call, the external procedures module 210 d calls the external routine in step 536. Specifically, the foundation services 204 create a connection with a listener agent (not shown) that controls the initiation of a plurality of the agent processes 300 on the remote computing system 322. The listener agent initiates the agent process 300, transfers the connection between the listener agent and the local server 202 to the agent process 300, and releases control of the agent process 300 to the foundation services 204. The agent process 300 then receives any necessary parameters from the external procedures module 210 d via the database link 310.

During execution of the external routine in the agent process 300, the agent process 300 may issue a callback query to the external procedures module 210 d, where the external routine executed by the agent process 300 requires an operation to be performed by the local server 202. In other words, the external routine may generate its own query to the local server 202. If the external procedures module 210 d receives a callback in step 538, the local server 202 coordinates transactions with the agent process 300 by suspending processing of the client statement in order to process the callback query in step 540. Thus, the callback query is performed within the same user session as corresponding to the request from the client 200. If necessary, the external procedures module 210 d may generate its own callback query to the agent process 300. Hence, if the external procedures module 210 d receives a plurality of statements from the agent process 300, the external procedures module 210 d suspends processing in the local server 202, and stacks the statements as received from the agent process 300, such that the callback goes to the same address space that executes the user's request. For every SQL statement, there is a context setup that contains the state of the SQL information. Hence, the process receiving the callback query (e.g., the local server process or the agent process 300) creates another cursor (context) such that there exists a stack of contexts. Hence, the external procedures module 210 d completes execution of each statement for a corresponding context before processing the next statement from the agent process 300.

After all the callback statements from the agent process 300 have been executed in step 540, the external procedures module 210 d receives the results from execution of the external routine by the agent process 300 in step 542, and the local server 202 completes execution in step 544 based upon the received results. According to the disclosed embodiment, completion of the statement for the client 200 results in the connection 310 between the local server 202 and the agent process 300 to be torn down, although the agent process 300 may be maintained and reinitialized for subsequent requests, if desired.

The present invention provides an architecture providing scaleable, efficient access to data in a heterogeneous database environment where the non-native characteristics of a distributed database system can be made transparent by the client. The agent process 300 provides a framework that allows for translation and transaction services to operate in a heterogeneous environment, where specialized modules provide dynamic translation services for respective database operations. The query services module provides dynamic translation of query statements between the client application and the foreign database systems, while the local server process maintains control of completing the statement. The transaction services module coordinates and manages transactions among the various database systems. In addition, use of database drivers for each foreign database system enables the disclosed architecture to utilize the full capabilities of the respective foreign database systems.

In addition, the disclosed architecture provides reliable execution of processes without risking the local server process operation by providing a plurality of agent processes executing in separate address spaces that communicate with the local server process via a database link. Hence, if a fault occurs in a foreign process, such as a foreign server instance or an agent executing an external routine, the link with the faulty process can be terminated without adversely affecting the local server process.

In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. 

What is claimed is:
 1. A method for processing a statement from a client, comprising the steps of: receiving the statement at a local database server specifying an operation to be performed at a foreign database server; determining whether the operation specified to be performed at the foreign database server is not implemented by the foreign database server; and if the operation is determined to be not implemented by the foreign database server, then causing the local database server to perform the steps of: determining one or more first operations to be performed by the local database server and one or more second operations to be performed by the foreign database server to execute the statement; sending a request to the foreign database server to perform said one or more second operations and to retrieve data stored in the foreign database server and needed to process said one or more first operations; and completing execution of the statement by performing said one or more first operations in the local database server based on retrieval of the data stored in the foreign database server and needed to process said one or more first operations.
 2. The method of claim 1, further comprising the steps of: accessing a first table in response to reception of the statement by the local database server, said first table specifying operations that can be performed by the foreign database server; and generating the request based on the operations that can performed by the foreign database server.
 3. The method of claim 2, further comprising the steps of: identifying said foreign database server based on the statement; and identifying the data stored in the foreign database server and needed to process one or more first operations.
 4. The method of claim 3, further comprising the step of including in the request a query to retrieve the data stored in the foreign database server needed to process said one or more first operations.
 5. The method of claim 1, wherein the step of sending the request to the foreign database server to perform said one or more second operations includes the steps of sending the request to an agent process in communication with the foreign database server.
 6. The method of claim 5, wherein the step of completing execution of the statement includes the step of receiving from the agent process a response to the request from the foreign database server, the response including the data stored in the foreign database server and needed to process said one or more first operations.
 7. The method of claim 5, further comprising: generating the request in a first format readable by the local database server process; converting the request in the agent process to a second format readable by the foreign database server; and sending the converted request having the second format from the agent process to the foreign database server.
 8. The method of claim 5, further comprising the step of initiating execution of the agent process by the local database server.
 9. The method of claim 5, wherein the step of causing the local database server process to determine at least one of said operations that can be performed by a foreign database server includes the step of causing the local database server process to determine at least one of said operations that can be performed by a foreign database server based on stored data describing capabilities of the foreign database server.
 10. A distributed database system configured to respond to a statement, comprising: a first computer system executing a local server process; and a second computer system, in communication with the first computer system, executing a foreign server process; wherein the local server process is configured for: receiving the statement, said statement specifying an operation to be performed by the foreign server process; determining whether the operation specified to be performed at the foreign server process is not implemented by the foreign server process; and if the operation is determined to be not implemented by the foreign server process, then performing the steps of: determining one or more first operations to be performed by the local server process and one or more second operations to be performed by the foreign server process; sending a request to the foreign server process to perform said one or more second operations and to retrieve data stored in the second computer system and needed to process said one or more first operations; and completing execution of the statement by performing said one or more first operations based on retrieval of data stored in the foreign server process and needed to process said one or more first operations; wherein the foreign server process is configured for receiving the request, performing said one or more second operations, and returning the results based on said performing said one or more second operations.
 11. The system of claim 10, further comprising a computer-readable medium storing a capabilities table specifying operations that are executable by the foreign server process.
 12. The system of claim 11, wherein the local server process is configured for sending the statement as the request to the foreign server process based on accessing the capabilities table.
 13. The system of claim 11, wherein the local server process is configured for determining said one or more second statements including one operation specified in the capabilities table and sending the request for the one operation to the foreign server process based on accessing the capabilities table.
 14. The system of claim 11, wherein the local server process is configured for generating a transaction message to the foreign server process based on corresponding transaction capabilities identified in the capabilities table.
 15. The system of claim 14, wherein the transactions coordinated between the local server process and the foreign server process include a distributed transaction between the local server process and the foreign server process.
 16. The system of claim 15, wherein the distributed transaction is a two-phase commit distributed transaction.
 17. The system of claim 10, wherein: the local server process executes in a first address space and the foreign server process is executed by an agent for performing an external routine in a second address space separate from the first address space; and said first computer system further comprises a heterogeneous services module that includes an external procedures module configured to initiate a connection with, and send the request to, the agent executing the external routine.
 18. The system of claim 17, wherein the heterogeneous services module includes foundation services configured to establish and maintain a connection with the agent process in communication with the foreign server process during execution of the statement.
 19. The system of claim 17, wherein the external procedures module is configured to pass arguments corresponding to the request to the agent for processing by the agent.
 20. The system of claim 17, wherein the local server process is configured for suspending execution of the statement in response to a query from the external routine and corresponding to the request.
 21. The system of claim 20, wherein: the external procedures module is configured to receive a plurality of said queries from the external routine during processing of the request, and the local server process recursively processes the queries within a singular instance.
 22. The system of claim 10, further comprising a computer-readable medium storing a data dictionary translation table specifying foreign data objects accessible by the foreign server process, wherein the heterogeneous services module is configured for translating an object in the statement to a corresponding one of the foreign data objects in response to accessing the data dictionary translation table, the request including the one foreign data object.
 23. The system of claim 10, wherein the local server process is configured for sending the request to the foreign server process to perform said one or more second operations by sending the request to an agent process in communication with the foreign server process.
 24. The system of claim 23, wherein the agent process is configured to control translation of the request from a first format readable by the local server process to a second format readable by the foreign server process.
 25. The system of claim 24, wherein the agent process includes a foreign database driver configured for providing the query services module with mapping information for the corresponding foreign server process for translating the request.
 26. The system of claim 25, wherein: the local server process is configured for mapping the request onto a format specified by an Application Programming Interface (API), and the foreign database driver is configured for translating the request from the format specified API to the second format.
 27. The system of claim 26, wherein foreign database driver is configured for translating the results received from the foreign server process from the second format in accordance with a format specified by the API, the query services module translating the results from the format specified by the API to the first format for the local server completing execution of the statement.
 28. The system of claim 26, wherein: the query services module is configured for communicating with a second foreign database driver providing mapping information for a second corresponding foreign server process and mapping a second portion of the statement from the first format to a format specified by the API, and the second foreign database driver is configured for translating the second portion of the statement from the format specified by the API to a third format readable by the second foreign server process.
 29. The system of claim 25, further comprising a plurality of agent processes having a plurality of said foreign database drivers providing mapping information for foreign server processes having prescribed formats, respectively, the query services module configured to map between the first format onto a format specified by an Application Programming Interface (API), each of the foreign database drivers configured to map between the format specified by the API and the format readable by the corresponding foreign server process.
 30. The system of claim 25, wherein: the agent process includes a second transaction module, complementary to the first transaction module, configured for mapping a transaction message from a first format readable by the local server process onto a format specified by an Application Programming Interface (API) for translation by a foreign database driver, and the foreign database driver is configured for translating the transaction message from the format specified by the API to a second format readable by the foreign server process for executing the transaction message.
 31. The system of claim 30, wherein: the second transaction module is configured for mapping a transaction response, generated by the foreign server process in response to executing the transaction message, from the format specified by the API to the first format, and the foreign database driver is configured for converting the transaction response from the second format to the format specified by the API.
 32. The system of claim 23, wherein the local server process is configured for initiating execution of the agent process by the local server process. 